1. Field of the Invention
The present invention relates to a display device called a head mount type display device or a spectacle-type display device for seeing an image of a display element such as a liquid crystal display element arranged immediately in front of the eye of the observer.
2. Description of the Related Art
A display device of this type is disclosed, for example, in Japanese Unexamined Patent Publications No. 5-134208, No. 5-210069, No. 5-328261, No. 7-46513, No. 9-189880, No. 11-64781 and Patent No. 2910111. Further, a display device including a light guide member is disclosed in Japanese Unexamined Patent Publications No. 2-297516, No. 5-304645 and No. 9-73043.
The display apparatus of this type comprises a display element such as a liquid crystal panel and an image-forming element such as a convex lens or a concave mirror for magnifying the image formed by the display element. FIG. 14 in the accompanying drawings is a view showing an optical system of the conventional spectacle-type display device. In FIG. 14, numeral 1 designates a display element, numeral 2 an image forming element, numeral 3 a virtual image of the display element 2 magnified by the image forming element 2, and numeral 4 the eye of an observer. The diffused light is illuminated on the display element 1, and the light passing through the display element 1 enters the pupil 4 of the observer through the image forming element 2. Thus, the observer can see the virtual image 3 of the display element 1 magnified by the image forming element 2. A diffusion surface la for generating the scattered light is arranged on the side of the display element nearer to the incident light source.
A fluorescent tube is used as a light source in this case. The fluorescent tube is large and heavy, and therefore it is difficult to use the fluorescent tube as the spectacle-type display device arranged immediately before the eye of the observer.
FIG. 15 shows an example in which a light emitting element 6 is used as a substantial point light source. The light emitting element 6 emits the divergent light. The divergent light that has passed through the display element 1 enters the pupil 4 of the observer as a convergent light through the image forming element 2. In this case, the divergent light is irradiated on the display element 1, and therefore the image forming element 2 is required to be arranged at a position near the display element 1. In view of the fact that the image forming element 2 is arranged at a position near the display element 1, however, the aberration increases to such an extent that the image quality is deteriorated. For this reason, as shown in FIG. 16, a plurality of image forming elements 2 and 2a are required to be arranged in order to improve the display quality. As a result, the problem is posed that the display device increases in size and becomes heavy as a whole.
Also, Japanese Unexamined Patent Publication No. 5-134208 described above proposes the use of an elliptical member having two focal points in order to realize a display device of a reduced size. Specifically, as shown in FIG. 17, a concave mirror 8 is formed utilizing a part of an elliptical member 7, so that the light passing through the display element 1 and a group of eccentric lenses 2xc3x97 passes through the first focal point P1 of the elliptical member 7, the light reflected by the concave mirror 8 passes through the second focal point P2, and the pupil 4 of the observer is arranged at the second focal point P2. By doing so, the light passing through the first focal point is reflected by the concave mirror 8, surely passes through the second focal point 2 and enters the pupil 4.
In the display device shown in FIG. 17, however, the display element 1 and the eccentric lenses 2xc3x97 are located beside the pupil 4 of the observer 4 and are liable to interfere with the side of the head (the portion near the ear) of the observer when the observer wears the display device. For this reason, the display device is required to be configured so that the display element 1 and the eccentric lenses 2xc3x97 may not interfere with the side of the head of the observer, and therefore the display device cannot be sufficiently reduced in size.
Also, in the configuration utilizing two focal points of the elliptical member 7, the display screen is liable to be distorted. Specifically, the angle of the light diverging from the first focal point P1 fails to coincide with the angle of the light focussed on the second focal point P2. Thus, in order that the angle of the light entering the pupil 4 may become the same as the angle of the light passing through the display element 1, a plurality of complicated eccentric lenses are required to be arranged as the eccentric lenses 2xc3x97 in the neighborhood of the display element 1. This poses the problem that the display device cannot be sufficiently reduced in size.
The present invention is intended to solve the aforementioned problems and the object thereof is to provide a display device which can be reduced in size and by which the observer can watch an image immediately before his eye.
Another object of the present invention is to provide a display device in which the image can be seen immediately in front of the eye of the observer and which can be configured in a manner not to interfere with the side of the head of the observer.
According to the present invention, there is provided a display device arranged in front of an eye of an observer comprising a light emitting element, a display element illuminated by the light emitting element, and an image forming element allowing the light passing through the display element to pass therethrough, wherein the display element is arranged between the image forming element and a first focal point at a position near the first focal point of the image forming element, whereby a virtual image of the display element is formed by the image forming element, and the light emitted from the light emitting element is focussed at a second focal point of the image forming element.
With this configuration, the image is focussed on the pupil of the observer and even a near virtual image is sufficiently visible as in a pinhole camera, thereby making it possible to provide a compact, inexpensive display device.
Further, according to another aspect of the present invention there is provided a display device comprising a display element, an image forming element, a first concave mirror formed as a part of a first elliptical member having a first focal point through which a light emitted from said display element and passing through said image forming element passes and a second focal point, and a second concave mirror formed as a part of a second elliptical member having a third focal point arranged at a position common to said second focal point and a fourth focal point, wherein the light emitted from said display element is focussed on or near said first focal point, the light passing through said first focal point is reflected by said first concave mirror and proceeds toward the common second and third focal points, and the light passing through said second and third focal points or the light equivalent thereto is reflected by said second concave mirror and focussed on or near said fourth focal point, so that the eye of the observer can be arranged on or near said fourth focal point to see an image on display formed in front of the eye of the observer.
With this configuration, by forming the first concave mirror and the second concave mirror using the first elliptical member and the second elliptical member with the second focal point and the third focal point located at the common position, and more preferably, by forming the first elliptical member and the second elliptical member as equivalent ellipsoid of revolutions, the symmetry of the optical system can be improved, and the need of using a plurality of complicated eccentric lenses is eliminated, unlike in the prior art, and the whole display device can be reduced in both size and weight.
Further, the present invention provides a display device with the aforementioned two features combined.
Furthermore, according to a further aspect of the present invention, there is provided a display device arranged in front of an eye of an observer comprising a display element, an image forming element for focussing a light emitted from the display element, a light guide element having an incident surface to which the light passing through the image forming element is made incident, and a concave mirror arranged on the light guide member for receiving the light passing through the light guide, wherein the concave mirror is formed as a part of an elliptical member having a first focal point and a second focal point, and the light passing through said image forming element is reflected a plurality of times in the light guide member and made incident to the concave mirror as if the light was made incident to said concave mirror from the second focal point, and the light reflected by said concave mirror is focussed on or near the first focal point, thereby entering the eye of the observer.
With this configuration, a compact display device having a simple structure can be obtained. In this case, the light guide member includes a pair of flat surfaces in opposed relation to each other, and an inclined surface at an angle to the flat surfaces. Preferably, the light passing through the image forming element is focussed on the inclined surface and reflected by a pair of the flat surfaces in opposed relation to each other. Also, preferably, the incident surface is the inclined surface or a part of the flat surfaces and the light made incident to the incident surface is reflected by the inclined surface.
Further, according to a further aspect of the present invention, there is provided a display device arranged in front of an eye of the observer comprising a display element, an optical element for converting a light illuminating said display element or a light passing through said display element into a substantially parallel light, and a concave mirror to which the light passing through said optical element is made incident, wherein said concave mirror is formed as a part of a paraboloid of revolution, and the light reflected by said concave mirror is focussed on or near the focal point of said paraboloid of revolution, thereby entering the eye of the observer.
With this configuration, a compact display device with a simple structure can be obtained. In this case, the optical element is preferably configured of another concave mirror formed as a part of the paraboloid of revolution. Also, the first concave mirror and the second concave mirror are preferably arranged on a light guide member.